Time resolved optical emission spectroscopy of an inductively coupled plasma in argon and oxygen

We present the space-time resolved excitation data for a single coil inductively coupled plasma (ICP) reactor operating in collision dominated regime in argon and oxygen at 13.56 MHz. Robot assisted scanning was used in order to obtain Abel inverted radial profiles of emission and subsequently of the net excitation rate as well as the number density of excited states. The net excitation rate in argon has modulation close to the walls due to the azimuthal field time dependence and a large bulk value independent of the time presumably due to low energy electron-metastable atom collisions. The time resolved profile in oxygen shows a much more pronounced modulation due to the azimuthal field and a much lower degree of excitation for the center of the tube. At low pressures a structure is observed in the temporal dependence of the net excitation rate that is consistent with two different mechanisms of electron acceleration with phase shift of π/4: (I) by azimuthal field and (II) due to the drift motion in crossed electric and magnetic fields that leads to a motion in the azimuthal or radial direction and consequently to energy gain.